Abstract: A filter housing assuring serial filtration of a liquid through plural filter cartridges and enabling flushing without requiring removal of the filter cartridges. The filter housing has a cap including a liquid inlet, a filtered liquid outlet, a flush liquid outlet, and internal passages. The filter cartridges are held within a canister which is pressed against the cap and constrained against rotation with the cap. A retaining member surrounding and bearing against the canister threads to the cap. The canister is divided into chambers, and has passages in its floor arranged to enable serial transfer of liquid from one chamber to the next. Flushing employs liquid introduced under normal pressure. Passages leading to the flush liquid outlet enable flushing to proceed when the flush liquid outlet is opened. At other times, filtered liquid will pass through passages leading to the filtered liquid outlet.